Federer does not want to ball bash but desperately wants to play with finesse and skill, and he has to have perfect timing to pull it off, and when he does he's masterful. I used to play with the Aeropro Drive, and switched to a Prestige 93, which was stupid. It wasn't conducive to my style I play. Federer's PS 90 is what he needs to play his game, and to reinforce that point Nadal would struggle mightily with that head size. His strokes are less precise and less technically sound, but he has a 100 so it doesn't matter. This isn't about head size at least I don't think so. But the only way to know for sure is if he does add a few sq. inches. I think Fed's struggles illustrate that the modern game is played with less risk and in terms of percentages that makes it tough for him.